Digital communication signals have international standards that define minimum signal thresholds for a binary one, or a high condition, and maximum signal thresholds for a binary zero, or a low condition. A standard for a particular type of communication signal typically also defines a transition time and/or voltage threshold as a reference, and specifies a time delay after the transition event during which to measure the data voltage in order to determine the validity of a particular bit. Therefore, if the signal level is lower than the high threshold or higher than the low threshold at this specified time, then the bit is not considered valid. Invalid bit transmissions increase network error rates, drive up maintenance costs, and may result in down time for the devices connected to the network or signal bus.
Minimizing or eliminating down time for the connected devices is especially important for Controller Area-based Networks (CAN), such as those based on the DeviceNet communication protocol, which may be employed in the context of an automated production line. DeviceNet industrial networks use the CAN interface as the backbone for a differential serial bus for bit communications and add a custom application layer. DeviceNet is defined by the Open DeviceNet Vendor Association standards and by International Standards Organization standard number ISO 11898. Typical devices interconnected via a CAN signal bus in a DeviceNet network include photo/optical sensors, proximity sensors, switches, as well as various other sensors and control units.
Existing DeviceNet network diagnostic devices have limited processing power and, therefore, typically collect only frame-level diagnostic information for storage in local memory. Such devices must be taken off-line in order to download data collected over time in the internal memory for further analysis. This prevents real-time analysis and network fault prediction since these devices do not interface with external networks and must first collect sufficient data prior to making it available (e.g., via a USB port connection). Furthermore, collection of frame-level information does not provide sufficient detail for waveform analysis that is needed to validate bit-level transmissions from particular network nodes.